Powered nailers and staplers are well known and have come into wide-spread use. This is true because they can drive fasteners more rapidly and more precisely than can be accomplished manually. In their most common form, such powered nailers and staplers are actuated by compressed air, necessitating the presence of an air compressor and long lengths of hose.
Recently, there has been much interest in electrically powered nailers and staplers, requiring only a source of electrical energy. Electrical energy is always present at a construction site. Such tools are also appropriate for the home market where electrical energy is readily available.
Prior art workers have devised many types of electro-mechanical fastener driving tools. For example, U.S. Pat. Nos. 4,042,036; 4,204,622; and 4,323,127 each teach an electric impact tool wherein the driver is frictionally moved through a working stroke by means of two counterrotating flywheels, each flywheel being provided with its own electric motor. U.S. Pat. No. 4,121,745 also teaches an electric impact tool utilizing counterrotating flywheels to frictionally move the driver through its working stroke. In this instance, however, one flywheel is directly driven by an electric motor, while the other flywheel is driven by the same electric motor through the agency of pulleys and an elastomeric belt or gear means.
U.S. Pat. Nos. 4,189,080 and 4,298,072 teach electro-mechanical fastener driving tools wherein the driver is moved through a working stroke by means of a single rotating, high-speed flywheel. The driver is engaged between the single flywheel and a support element. The preferred form of support element comprises a low inertia roller. Both patents teach, however, that other support means, such as a linear bearing or a Teflon block, could be used to accomplish the same purpose.
Electro-mechanical tools of the general class described above can be used to drive nails, staples or the like. For purposes of an exemplary showing, the present invention will be described in terms of its application to an electro-mechanical nailer. It will be understood by one skilled in the art, however, that the teachings of the present invention are equally applicable to electromechanical staple driving tools.
All such electro-mechanical fastener driving tools share a common problem. This problem is one of build-up of foreign material on the driver and transfer of the foreign material from the driver to the flywheel. Ultimately, a good drive is no longer possible because friction between the driver and the flywheel is lost.
For example, it is common practice to arrange the nails in the tool magazine in parallel-spaced relationship and to maintain them in this relationship through the use of strips of tape coated with a thermoplastic hot melt glue. It is also common practice to coat at least the initial driven portion of each nail shank with a resin based coating, or the like, to assist the nail's penetration of the workpiece and to increase the nail's holding power, once driven.
Since the driver is moved through its working stroke by means of frictional engagement with at least one flywheel, the driver will tend to get hot during use of the tool. In fact, the driver gets hot enough to melt the hot melt glue or the coating on the nail, or both. As the driver moves between the flywheels (or the flywheel and a back-up means) under a squeeze force, the melted material builds up in front of the driver-flywheel contact area until a planing or floating action occurs, and the driver-flywheel contact is actually reduced enough to lose friction and thus the driving force. Under these circumstances, driver power can only be restored by disassembling the tool and cleaning the driver and the one or more flywheels.
The present invention is based upon the discovery that if the flywheel is provided with circumferential grooves (or both flywheels are provided with circumferential grooves, where two flywheels are used), a build-up of foreign material resulting in a loss of friction between the one or more flywheels and the driver will not occur. The grooves are provided while maintaining the optimum total contact area between the one or more flywheels and the driver. The grooves provide voids along the driver-flywheel contact line into which the foreign material tends to flow. As a result, a positive frictional engagement of the driver by the one or more flywheels is achieved cycle-after-cycle. The working life of the one or more flywheels, and particularly the working life of the driver, are greatly increased. This is true because wear of the flywheels, and particularly the driver, is minimized.